The present invention relates to an input data processor for a D/A (Digital to Analog) converter, and more particularly to an input data processor for a D/A converter which is suitable for an information reproducer for a record medium such as an optical disk or the like having digital signals as recorded information.
D/A converters are generally used in digital audio equipment such as CD (Compact Disk) players or the like for the purpose of converting the digital data recorded in CD players into analogue signals. D/A converters generate quantizing noise by switching operation. As such quantizing noise includes higher harmonics of higher order to cause waveform distortion thereby to hinder faithful reproduction. In order to prevent the generation of such quantizing noise, a dither signal is conventionally added to the digital data read from a CD player.
In CD players, data is expressed by using 2's complement data. In a case of 2's complement data, inversion of MSB (Most Significant Bit) is performed at each time digital data crosses the zero level during conversion by a D/A converter. During the MSB inversion, switching noise called glitch is generated.
Such glitch is noise naturally generated in the D/A converter, and the use of a dither circuit causes such glitch to be increased by vibration of the dither signal. This phenomenon is caused by an increase in the number of times of zero crossing in correspondence with the vibration of the dither signal. When the D/A conversion output containing such glitch is introduced into a low pass filter, the output signal is integrated in the low pass filter to produce a distorted waveform. Particularly, when the original signal is a low level of signal, this has a significant effect and causes a reduction in the fidelity of reproduction.